Lasers are used in a wide variety of applications. In particular, lasers are integral components in optical communication systems where a beam modulated with vast amounts of information may be communicated great distances at the speed of light over optical fibers.
Of particular interest is the so-called vertical cavity surface emitting laser (VCSEL). As the name implies, this type of laser is a semiconductor micro-laser diode that emits light in a coherent beam orthogonal to the surface of a fabricated wafer. VCSELs are compact, relatively inexpensive to fabricate in mass quantities, and may offer advantages over edge emitting laser which currently comprise the majority of the lasers used in today's optical communication systems. The more traditional type edge emitting laser diodes emit coherent light parallel to the semiconductor junction layer. In contrast, VCSELs emit a coherent beam perpendicular to the boundaries between the semiconductor junction layers. In other words, VCSELs emit a beam in a vertical direction from the substrate as opposed to emitting a beam in the same plane as the substrate. Among other advantages, this may make it easier to couple the light beam to an optical fiber and may be more efficient.
VCSELs may be efficiently fabricated on wafers using standard microelectronic fabrication processes and, as a result, may be integrated on-board with other components. VCSELs may be manufactured using, for example, aluminum gallium arsenide (AlGaAs), gallium arsenide (GaAs), indium gallium arsenide nitride (InGaAsN), or similarly suited materials. VCSELS have been successfully manufactured in 850 nm, 1310 nm and 1550 nm ranges. This allows for a wide variety of fiber optic applications ranging from short reach applications to long haul data communications. VCSELs are promising to advance optical communication systems by providing a fast, inexpensive, energy efficient, and more reliable source of laser beam generation.
VCSELs are low cost laser which has been widely used in the optical transceivers. One of the challenges is the reliability of VCSEL. For example, it is estimated that the cumulative failure percentage for a 850 nm VCSEL may be about 2.33% at 12624 hours (1.44 years) with burn-in condition (100° C. and 20 mA). Even with low forward drive current (e.g. 10 mA DC) and low temperature (e.g. 40° C.), the cumulative failure rate is still about 1% around 11.4 years for the VCSEL built in the last decade. As a practical matter, the failure rate is likely much higher since typical operation conditions in the real world is about 18 mA AC driving current at 60-70° C. At 70° C., the cumulative failure rate is a factor of 8.4 lower than 40° C., which is about 1% at 1.35 years.
As the industry drives the communication bit rate faster and faster, VCSEL arrays were built for parallel optical transceivers, which made it even harder to control the quality and reliability. On other hand, the VCSELs are typically driven harder to boost the high speed performance, which dramatically reduces the VCSEL lifetime.